The instant invention relates to thermally actuated switching devices and more particularly to a thermally actuated latch which is permanently actuatable for completing an electrical circuit in response to exposure to a predetermined elevated temperature condition.
A variety of different types of devices which are actuatable in response to predetermined elevated temperature conditions have been heretofore available. For example, the U.S. Pat. Nos. 4,065,741 to Sakamoto, 3,952,274 Plasko; 3,956,725 Merrill et al; 3,291,945 Merrill et al; 4,145,654 Grimm; 4,186,366; McVey 4,307,370 Hollweck; and 4,472,705 to Carlson, and the European patent application No. 80300246.8, to Eaton disclose devices which represent the closest prior art to the subject invention of which the applicant is aware and which are fusible in response to predetermined elevated temperature conditions for interrupting electrical circuits. Devices of the type disclosed in these references have generally been found to be effective for interrupting various circuits in order to alleviate high-temperature overload conditions. However, while the above devices have been found to be effective, they have not been operative for closing circuits in response to elevated temperature conditions. Further, it has been found that there is a significant need for an effective device for permanently closing various electrical circuits in response to high-temperature conditions. For example, it has been found that there is a need for an effective device for permanently actuating audible and/or visible alarms and other indicator devices in order to alert operators to the fact that high-temperature overload conditions either exist or have existed and that certain other circuitry components may therefore require replacement. It has also been found that there is a need for an effective device for closing circuits in order to actuate various personnel and/or equipment protection systems, including fireprotection systems and fire door opening mechanisms, in response to high-temperature conditions. In this regard, while conventional thermostatic switching devices have been heretofore available for closing circuits in response to high-temperature conditions, it has been found that there is nevertheless a need for a positively and permanently actuatable device for closing circuits in response to various predetermined high-temperature conditions.
The instant invention provides an effective device which is permanently actuatable for closing electrical circuits in response to predetermined high-temperature conditions. More specifically, the instant invention provides a thermally actuated latch comprising a base portion, a fixed contact on the base portion, a resiliently movable contact arm having a movable contact thereon which is resiliently biased to a position wherein it engages the fixed contact, and deformable means communicating with the contact arm to normally maintain the movable contact in spaced relation to the fixed contact. The deformable means, preferably comprises a fusible pellet, and it is deformable upon exposure to a predetermined elevated temperature to enable the movable contact to move to a position of engagement with the fixed contact. The thermally actuated latch preferably further comprises a housing having a wall portion, a communicator disc in the housing, and a fulcrum on the base portion; and the fusible pellet is preferably mounted in the housing adjacent the wall portion. Specifically, the fusible pellet is preferably mounted so that it communicates with the movable contact arm through the communicator disc for normally maintaining the movable contact arm in a position wherein it is pivoted on the fulcrum to maintain the movable contact in spaced relation to the fixed contact. The communicator disc is preferably mounted in the housing so that it is also operative for substantially isolating the deformable means from the spaced and movable contacts to prevent the deformable means from interfering with the engagement of the fixed and movable contacts in the event that the fusible pellet is fragmented or partially melted before the movable contact is moved into engagement with the fixed contact. The movable contact arm is preferably embodied as an integrally struck portion of an actuator disc comprising a peripheral rim portion and the movable arm, and the arm preferably extends substantially radially inwardly from the rim portion. Further, the communicator disc preferably communicates with the rim portion of the actuator disc adjacent the end of the movable arm for normally maintaining the movable arm in a position wherein it is pivoted on the fulcrum to maintain the movable contact in spaced relation to the fixed contact.
The thermally actuated latch of the subject invention effectively solves the problem of providing a reliable latching device which is permanently actuatable for closing an electrical circuit in response to a high-temperature condition. Specifically, the communicator disc and the actuator disc cooperate for maintaining the fixed and movable contacts well spaced apart during normal operations. However, in the event of a high-temperature condition, the fusible pellet is deformable to a disposition of reduced profile to enable the movable contact to positively engage the fixed contact and to thereby close an electrical circuit connected to the latch. In this connection, the actuator disc, the communicator disc and the fulcrum cooperate to amplify the movement of the movable arm to normally maintain the movable contact in well spaced relation to the fixed contact in order to prevent arcing. Further, the communicator disc physically isolates the fusible pellet from both the movable and fixed contacts to insure that they are not contaminated before they are moved to a closed position.
Accordingly, it is a primary object of the instant invention to provide an effective and reliable latching device for closing an electrical circuit in response to a high-temperature condition.
Another object of the instant invention is to provide an effective permanently actuatable latching device for closing an electrical circuit in response to a high-temperature condition.
Other objects, features and advantages of the invention shall become apparent as the description thereof proceeds when considered in connection with the accompanying illustrative drawings.